This invention relates to superhard cutting elements useful in rock drilling and machining wear resistant materials. Specifically, this invention relates polycrystaline diamond and cubic boron nitride cutting elements produced by means of high pressure and high temperature. Although these two super materials have divergent properties, it is not uncommon in the literature to speak in terms of one or both when addressing common issues. Since the issues raised in this application apply generally to both materials, the application will speak in terms of a superhard material. Those skilled in the art will readily understand the utility of this invention as it applies to both supermaterials.
Superhard cutting elements are now so widely accepted in the drilling and tooling industries that they have become the standard and preferred tool for difficult applications. But these tools are not without limitations. Superhard materials have high hardness and abrasion resistance, but generally speaking, standing alone, they lack the toughness required by most difficult drilling and cutting jobs. By mounting the superhard material on a tough substrate, such as tungsten carbide, a certain amount of synergism is achieved; the superhard cutting element acquires the toughness of the substrate to go along with the hardness and abrasion resistance of the superhard material, itself.
In the art, varied attempts have been made to improve the utility of superhard cutting elements. These efforts have largely centered on improving the bond between the substrate and the superhard material. An example of this issue is addressed but not fully taught in U.S. Pat. No. 5,460,233. The problem ostensibly addressed in that patent was to provide a means of protecting the cutting table of a rock drilling element from damage as the cutting element first contacted formation being drilled. That is to say, as the bit was lowered into the hole and impacted the formation to be drilled, there was a tendency for the superhard surface of the cutting elements to fracture and delaminate. The applicants discovered that by contouring the substrate away from the superhard cutting surface, they were able to sufficiently protect the superhard materials long enough for it to wear into a safe mode. The published data showed that the substrate thus configured could withstand more than double the WOB of conventional cutting elements. What the disclosure failed to find was a means of actually imparting the toughness of the substrate into the superhard cutting table itself.
Therefore, it would be useful to provide a means for reinforcing the superhard cutting surface and give it the toughness inherent in the tungsten carbide substrate, while at the same time providing an inherently tougher superhard cutting surface.